The following abbreviations that may be found in the specification and/or the drawing figures are defined as follows:
3 GPP third generation partnership project
BCCH broadcast channel
DL downlink (network towards UE)
E-DCH enhanced dedicated (physical) channel
E-DPCCH enhanced dedicated physical control channel
E-DPDCH enhanced dedicated physical data channel
E-HICH E-DCH HARQ acknowledgement indicator channel
E-RGCH E-DCH relative grant channel
E-RNTI E-DCH radio network temporary identifier
FACH forward access channel
HARQ hybrid automatic repeat request
H-RNTI HS-DSCH radio network temporary identifier
HSPDA high speed downlink packet access
HS-DSCH high speed downlink shared channel
HS-DPCCH high speed dedicated physical control channel
NCL neighbor cell list
NodeB base station
RF radio frequency
RNC radio network controller
RRC radio resource control
SI system information
SIB system information block
UE user equipment
UL uplink (UE towards network)
UTRAN universal terrestrial radio access network
Continuing improvements of the UTRAN system have recently included the investigation of a CELL-FACH enhancement which in part intends to improve cell reselection. A UE in the CELL-FACH state has no dedicated physical channel allocated to it, but instead it continuously monitors the FACH in the DL and is assigned a random access channel RACH for accessing an uplink transport channel. While in the CELL-FACH state the UE can have only one serving cell, and so it performs cell reselection according to specified reselection rules, typically to change the current serving cell to a better quality neighbor cell.
In current specifications the UE does this by first obtaining the system information of the neighbor cell (typically 1.28 seconds) then sends a cell update message upon cell reselection while in the in CELL-FACH state so that the network can provide a dedicated resource on the new serving cell for the UE. The network provides this resource in a Cell Update Confirm message, and the cell update procedure can take up to a full second to perform. These conventional procedures are detailed at 3GPP TS 25.331 v10.3.1 (2011-04) subclause 8.3.1. But until this cell update procedure is complete, the UE cannot perform dedicated data transmission and reception and so there is a time, on the order of up to a few seconds, during which service is disrupted due to the cell reselection.
Also, in Release-8 of UTRAN there was introduced an “Enhanced Uplink in CELL-FACH state and idle mode” feature, by which the UE cannot perform cell reselection when it has an uplink resource allocated to it by the network. So a UE capable of this enhanced uplink in CELL-FACH state and idle mode is at risk of losing its synchronization to its serving cell due to that cell reselection restriction. It is expected that the CELL-FACH enhancement noted above will address this particular issue (e.g., in 3GPP Release 11) by allowing reselection during an ongoing E-DCH transmission. But still some improvements are required to enable this while avoiding or minimizing other problems.
Finally, another problem arises where the UE's reception of both the serving cell and the detected neighbor cells are all relatively weak. In this case reception on only a single cell would be unreliable, and potentially under some fading conditions the UE may reselect back and forth between difference cells in a kind of ping-pong effect as a result of poor signal reception which is only transient at the UE. Reception from multiple cells simultaneously would increase the reliability since the UE could then combine the successful reception from different cells. On balance this could potentially reduce the uplink signaling load since the UE would engage in fewer total reselections and corresponding cell update procedures.
Exemplary embodiments detailed below with particularity provide solutions to the above problems in that they detail UE and network actions for multipoint reception at the UE in the CELL-FACH state from multiple network cells.